Pressure sensitive mine insensitive to water deactivation

ABSTRACT

A pressure sensitive explosive composition is provided which is rendered insensitive to water or water vapor by means of a coating of an organo-functional silane capable of polymerization on contact with water or water vapor. Additionally, a method is provided of coating such a composition by the use of the abovementioned silane in a halocarbon solvent having a relatively low vapor pressure at ambient conditions. The composition may be a mixture of an inorganic oxidizer and fuel such as potassium chlorate, red phosphorous and ground glass or a mixture of a primary explosive such as lead azide and a secondary explosive such as RDX, either mixture being coated with a silane such as gamma ( Beta aminoethyl) aminopropyl trimethoxy silane applied from a volatile halocarbon liquid such as 1,1,2 trichloro-1,2,2 trifluoro ethane. The silane, after evaporation of the liquid, coats the composition and polymerizes on contact with water or water vapor to form a water impermeable film and this renders the composition insensitive to water deactivation.

United States Patent 91 Seals [451 Jan. 22, 1974 PRESSURE SENSITIVE MINEINSENSITIVE TO WATER DEACTIVATION William O. Seals, Budd Lake Heights,NJ.

22 Filed: May 22,1973

21 Appl. No.: 362,721

Related U.S. Application Data [62] Division of Ser. No. 226,545, Feb.15, 1972.

[75] Inventor:

[52] U.S. Cl. 102/8, 102/7.2 [51] Int. Cl. F42b 23/14 [58] Field ofSearch 102/72, 8

[56] References Cited UNITED STATES PATENTS R27,025 1/1971 McDonald149/11 X 2,368,310 1/1945 Lecky et a1. 102/8 UX 2,999,744 9/1961 Eckels149/19 3,138,100 6/1964 Peschko 102/8 3,190,775 6/1965 Ender 149/83,667,387 6/1972 Picard et al..... 102/8 3,738,276 6/1973 Picard et a1102/72 Primary Examiner-Carl D. Quarforth Assistant ExaminerE. A. MillerAttorney, Agent, or F irm-Edward J. Kelly; Herbert Ber]; A. VectorErkkila [5 7] ABSTRACT A pressure sensitive explosive composition isprovided which is rendered insensitive to water or water vapor by meansof a coating of an organo-functional silane capable of polymerization oncontact with water or water vapor. Additionally, a method is provided ofcoating such a composition by the use of the abovementioned silane in ahalocarbon solvent having a relatively low vapor pressure at ambientconditions. The composition may be a mixture of an inorganic oxidizerand fuel such as potassium chlorate, red phosphorous and ground glass ora mixture of a primary explosive such as lead azide and a secondaryexplosive such as RDX, either mixture being coated with a silane such as7(B aminoethyl) aminopropyl trimethoxy silane applied from a volatilehalocarbon liquid such as 1,1,2 trichlorol ,2,2 trifluoro ethane. Thesilane, after evaporation of the liquid, coats the composition andpolymerizes on contact with water or water vapor to form a waterimpermeable film and this renders the composition insensitive to waterdeactivation.

7 Claims, No Drawings PRESSURE SENSITIVE MINE INSENSITIVE TO WATERDEACTIVATION BACKGROUND OF THE INVENTION For certain battlefieldapplications, it is desirable to deploy a largenumber of packagedexplosives over a pre-selected area of the battlefield. Aircraftdispersal is the most convenient method of deployment. This type ofdispersal requires maintenance of the packages in a substantiallyinsensitive state until after they hit the ground. An effective,economical method for fabrication of these packages is accomplished byplacing the explosive in a vapor permeable container and filling thecontainer with a desensitizing liquid, which will permeatexthecontainer. After the package is deployed the liquid will evaporatethrough the container and leave the enclosed explosive armed. One of theprincipal drawbacks of this type of system is the possibility ofpremature desensitization of the explosive by water or water vapor. Forexample, rainfall will cause moisture permeation of the package andpermanently desensitize the explosive before it can effectivelyfunction. Additionally, a very humid atmosphere has a strong tendency toeffect premature complete desensitization due to permeation of thepackageby water vapor.

The difficulty thus encountered is of relatively recent originandalthough many organic compounds, including silanes and siloxanes havebeen used for various purposes with energetic components (see forexample U. S. Pat. Nos. 3,551,222; 3,404,061; 3,058,858; 3,190,775;3,190,776 and 3,110,638), these uses were neither analogous to theinstant problem nor indicative of a solution thereto.

It is, therefore, an object of this invention to provide an; explosivecomposition which is insensitive to moisture.

Another object is to furnish a method of rendering an explosivecomposition insensitive to moisture.

A further object is to provide a moisture insensitive, pressuresensitive, explosive composition for use in antipersonnel mines.

Other objects and many of the attendant advantages of thislinventionwill be readily appreciated as the same become better understood byreference to th following description, wherein it, is shown that theabovementioned objects are attained and the prior art deficiencies areovercome by the use of an organofunctional silane monomer in a solventsolution to coat allof the components of an explosive composition andthus render the composition insensitive to water vapor, or water.

DESCRIPTION OF A PREFERRED EMBODIMENT Certain types of mines have beenused which are dispersed over a preselected area of a battlefield by airdrop. These mines must be maintained in an insensitive condition untilthey hit the ground. One advantageous method of accomplishing this is byusing a pressure sensitive explosive or pyrotechnic composition immersedin a desensitizing liquid, the whole being enclosed in a container whichis permeable to the vapor of the desensitizing liquid. By the use ofthis method the mines could be deployed while insensitive and thenbecome armed through the evaporation of the desensitizing liq uid. Onstanding in a human atmosphere or in a rainstorm, the containedexplosive or pyrotechnic tended to become inert because of sorption ofwater vapor or actual inundation by rain water. I have found that byadding a soluble, organo-functional silane monomer, which polymerizes oncontact with water vapor, to the desensitizing liquid and by intimatelymixing the resultant solution with the selected explosive or pyrotechniccomposition, a mixture is formed which will leave a coating of silanemonomer on the explosive composition when the desensitizing liquidvolatilizes on standing. Since the monomer polymerizes on contact withwater vapor and since the polymer thus formed is not permeable to wateror water vapor, this coating provides a means of making the explosive orpyrotechnic composition insensitive to moisture. I have also found thatthis polymer coating does not interfere with the pressure sensitivitynecessary to ultimately activate a mine.

Indeed, my invention need not be used exclusively with a mine, it may beused with any compatible explosive or pyrotechnic composition which mustbe protected from moisture either vapor or liquid.

The solvent liquid used with my invention must be capable of dissolvingthe silane monomer and additionally possess the properties ofnon-reactivity and nonsolvation with the explosive, non-reactivity withthe organo-functional silane monomer and a vapor pressure, such that theliquid will evaporate in a relatively short time at ambienttemperatures, thus in effect resulting in a reversibly desensitizedmine. Additionally, if my invention is to be used with the type of minedescribed, the liquid solvent must be capable of desensitizing theexplosive or pyrotechnic while the explosive is still thoroughly wettedby the liquid. Any liquid which will meet these critera can be used.

It has been found that halocarbons of a chain length of one or twocarbon atoms containing at least one halogen substituent are preferable,for example Freon l 13 or perchloroethylene. These halocarbonspreferably have a boiling point between about 30C and about C. Otherpreferred halocarbons are 1,1,2 trichloro-l,2,2 trifluoroethane; l,l,2,2tetrachloro-l,2 difluoroethane; l,1,2,2 tetrafluoro-1,2 dibromoethane;carbon tetrachloride and tetrachloroethylene. Additionally, when theorgano-functional silane is a liquid of sufficiently low viscosity, itcan be readily mixed with the explosive and it will not be necessary touse a desensitizing liquid. This procedure, although effective is notpreferred because of attendant hazardous mixing conditions. My inventioncan be utilized for protection of any solid explosive compositionsusceptible to desensitization by moisture, for example: mixtures of redphosphorous, a strong inorganic oxidizer such as potassium chlorate orperchlorate and ground glass and pressure sensitive mixtures of primaryexplosives such as lead azide or lead styphnate and secondary explosivessuch as RDX, PETN or l-IMX.

My invention utilizes organo-functional silane monomers capable ofreacting with moisture at atmospheric temperatures to form a waterimpermeable polymer. The monomer must be soluble in the desensitizationliquid and adhere strongly to the solid explosive or pyrotechnicsubstrate. This is usually accomplished either during the immersion ofthe substrate in the liquid or upon substantial volatilization of theliquid thus leaving a monomeric coating. Additionally, the monomer mustbe capable of forming a moisture impervious coating of polymer uponcontact with water or water vapor. Further, the coating must not preventinitiation of the explosive. The total amount of silane monomer usedwill depend on the amount of surface area of explosive substrate becausea complete coating is desired. Additionally, the amount used must not beenough to cause excessive desensitization. l have found that betweenabout 1 percent and percent by weight of monomer, based on the amount ofexplosive or pyrotechnic substrate, will give satisfactory results. 2percent by weight is preferred. Organo-functional silanes capable of usewith my invention are well known and can be represented by the generalformula.

wherein Si represents a silicon atom, at least one of the R substituentsis selected from the group consisting of halogen, amino, alkoxyandaryloxy and R represents a substituent selected from the groupconsisting of alkyl, aryl, aminoalkyl, aminoaryl, alkylamino, arylamino,alkoxy and aryloxy and n is an integer from 1 to 3 inclusive. Generally,the reaction of such an organo-functional silane to effect protectionagainst moisture for the composition of my invention is thought to be ahydrolytic polycondensation which is believed to proceed largely asfollows:

wherein R, R anTd n have the aforementioned definitions. The silanolproduct of reaction (1) is unstable and reacts further to form apolymeric silicon containing material. In some cases a siloxane isformed, in other cases a cyclic polymer and in yet others apolyorganosiloxane. The type of polymer formed depends upon the type andnumber of the R and R substituents. R is selected for its ability tohydrolyze to form the necessary intermediate silanol and R is selectedfor its ability to lend water impermeability to the formed polymer.Generally, where R is alkoxy it will be a short chain, i.e., from one tofour carbon atoms. Additionally, the polymerization rate also depends onthe substituents selected. Since the purpose of my invention is broadlyto provide protection against water and water vapor, the polymerizationrate should be relatively rapid upon contact with water or water vapor.

Some examples of silanes that may be used with my invention, follow: y(Baminoethyl) aminopropyl trimethoxy silane; 'yaminopropyltriethoxysilane; methyl triethoxysilane; phenyltrichlorosilane;nbutyltrichlorosilane; dimethyl dichlorosilane and methylphenyldichlorosilane.

in certain cases catalysts which are soluble in the liquid used as adesensitizing solvent may be added to insure polymerization of themonomer if they are compatible with the ultimate function of theexplosive or pyrotechnic composition.

The method and composition of this invention, which may be used toproduce a safe desensitized explosive item having the propertiesdesired, are set forth in the following examples. It is, of course,understood that these examples are meant to be illustrative and notrestrictive of my invention.

EXAMPLE 1 A one percent solution of y (/3 aminoethyl) aminopropyltrimethoxy silane in 10 cc. of 1,1,2 trichloro- 1,2,2 trifluoro ethanewas prepared under dry conditions. 0.2 gram of fumed silica thickeningagent and then 5 grams of potassium chlorate were added to the solutionwith agitation. 2 grams of red phosphorous were then added and theresulting desensitized slurry was agitated until homogeneous. 1 gram ofcut pyrex glass was added to a small polyethylene* cup under dryconditions and dampened with 1,1,2 trichloro- 1 ,2,2 trifluoro ethane. 3grams of the desensitized slurry was added to the cup and then the cupwas closed with a rigid polyethylene disc and heat sealed. The cup wasconditioned at a specified temperature and relative humidity andsubsequently tested for effectiveness by standard tests.

The polyethylene cup and disc were made from Alathon A 3120 film (aregistered trademark of E. l. DuPont de Nemours Co.), this product,marketed by DuPont, was found suitable for the present application.

EXAMPLE 2 Using the same procedure as in Example 1, but in place of thepotassium chlorate, red phosphorous and ground glass, enough RDX andlead azide is introduced into the halocarbon, silane, silica slurry toform a final mixture containing 60 parts by weight of RDX to 40 parts byweight of lead azide.

RESULTS Ten of the cups were prepared by the method of Example l, andallowed tostand at ambient temperature and humidity until the solventwas removed by evaporation. After a predetermined time five of the cupswere detonated and the pressure required to cause detonation wasrecorded. The pressure required to initiate the detonation of the cupsfell' between 6 and 8 psi which compared favorably with control cupsidentically prepared without the silane additive. The remaining fivecups were placed in a percent relative humidity chamber at roomtemperature for humidity testing. Two cups were removed after 7 days andtested; one of the cups detonated at 6 psi, the other required 16 psi.Three cups were removed after 14 days in the chamber and tested; one ofthe cups detonated at 9 psi, the other two required 38 psi and 40 psirespectively.

These results indicate that there is no apparent desensitization of theexplosive by the addition of silane as shown by the comparability of thepressure required to detonate the test cups and the pressure required todetonate control cups prepared without silane. Additionally, with the 7day test, since one of the samples was in line with the necessarystandard control pressure, the indication is that the silane hasprovided water vapor protection. The second result which was high mayindicate poor coverage by the silane due to inhomogeneity of theoriginal mixture. The test after 14 days indicates the same water vaporprotection evident in one of the samples while the other two highresults may again indicate inhomogeneity.

Thus, it can be seen that the use of my invention,

, wherein an explosive composition is coated with a water;reactiveorgano-functional silane monomer to prevent detrimental contactof the explosive by moisture, forms the basis for an advance in the art.

I wish it to be understood that I do not desire to be limited to theexactdetails described, for obvious modification will occur to a personskilled in the art.

I claim:

1. A reversibly desensitized antipersonnel mine comprising:

a slurry of a particulate, normally pressure and moisture sensitiveexplosive composition in a solution of an organo-functional silanemonomer, capable of reacting with atmospheric moisture at atmospherictemperatures to form a water impermeable polymer, ina halocarbon liquidcapable of desensitizing said explosive composition, said halocarbonhaving a boiling point between about 30C and 120C, and a sealedcontainer enveloping said slurry, said container, being vapor permeableto both atmospheric moisture and said halocarbon liquid, whereby ondeployment of said mine said halocarbon liquid evaporates through saidpermeable container and deposits a coating of said silane monomer onsaid particulate explosive composition, and atmospheric moisture entersthrough said permeable container and reacts with said silane to form awater impermeable polymer rendering said normally pressure sensitiveexplosive composition insensitive to moisture.

2. A mine as defined in claim 1 wherein said halocarbon is a halogenatedhydrocarbon and said hydrocarbon is selected from the group consistingof methane,

ethane and ethylene.

3. A mine as defined in claim 2 wherein said halocarbon is selected fromthe group consisting of 1,1,2 trichloro-l ,2,2 trifluoroethane; l,l,2,2tetrachloro-l ,2 difluoroethane; l,l,2,2 tetrafluoro-l ,2 dibromoethane;carbon tetrachloride and tetrachloroethylene.

4. A mine as defined in claim 1, wherein said explosive composition isselected from the group consisting of a mixture of an inorganicoxidizer, red phosphorous and ground glass and a mixture of a primaryexplosive selected from the group consisting of lead azide and leadsyphnate and a secondary explosive selected from the group consisting ofRDX, PETN andVHMX.

5. A mine as defined in claim 4 wherein said inorganic oxidizer isselected from the group consisting of potassium chlorate and potassiumperchlorate.

6. A mine as defined in claim 1 wherein said organo functional silanemonomer has the general formula wherein R is a radical selected from thegroup consisting of halogen, amino, alkoxy and aryloxy, R is a radicalselected from the group consisting of alkyl, aryl, aminoalkyl,aminoaryl, alkylamino and arylamino, and n is an integer from 1 to 3inclusive.

7. A mine as defined in claim 6 wherein said organofunctional silanemonomer is selected from the group consisting of 'y (/3 aminoethyl)aminopropyl trimethoxy silane, 'y aminopropyl triethoxy silane, methyltriethoxysilane, phenyltrichlorosilane, n-butyl trichlorosilane,dimethyl dichlorosilane and methyl phenyl dichlorosilane.

2. A mine as defined in claim 1 wherein said halocarbon is a halogenatedhydrocarbon and said hydrocarbon is selected from the group consistingof methane, ethane and ethylene.
 3. A mine as defined in claim 2 whereinsaid halocarbon is selected from the group consisting of 1,1,2trichloro-1,2,2 trifluoroethane; 1,1,2,2 tetrachloro-1,2 difluoroethane;1,1,2,2 tetrafluoro-1,2 dibromoethane; carbon tetrachloride andtetrachloroethylene.
 4. A mine as defined in claim 1, wherein saidexplosive composition is selected from the group consisting of a mixtureof an inorganic oxidizer, red phosphorous and ground glass and a mixtureof a primary explosive selected from the group consisting of lead azideand lead syphnate and a secondary explosive selected from the groupconsisting of RDX, PETN and HMX.
 5. A mine as defined in claim 4 whereinsaid inorganic oxidizer is selected from the group consisting ofpotassium chlorate and potassium perchlorate.
 6. A mine as defined inclaim 1 wherein said organo-functional silane monomer has the generalformula R(4 n) - Si - R''n wherein R is a radical selected from thegroup consisting of halogen, amino, alkoxy and aryloxy, R'' is a radicalselected from the group consisting of alkyl, aryl, aminoalkyl,aminoaryl, alkylamino and arylamino, and n is an integer from 1 to 3inclusive.
 7. A mine as defined in claim 6 wherein saidorgano-functional silane monomer is selected from the group consistingof gamma ( Beta aminoethyl) aminopropyl trimethoxy silane, gammaaminopropyl triethoxy silane, methyl triethoxysilane,phenyltrichlorosilane, n-butyl trichlorosilane, dimethyl dichlorosilaneand methyl phenyl dichlorosilane.